It is known that ultrasonic measurements provide the thickness of a component by measuring the time (T) that an ultrasonic signal takes to propagate across a component (1) and return to the ultrasound equipment (2). FIG. 1 shows this technique, wherein the thickness of the component (E) is calculated by the formula E=V·T/2, wherein (V) is the ultrasound speed set at the ultrasound emitter (2).
Since the measurement accuracy of each ultrasound speed is different for different thickness to be measured, standard use of ultrasonic automatic equipment for measuring the thickness of a component having areas of different thickness, conventionally requires several adjustments of the generated ultrasonic speed (V) for maximum and minimum thickness of that particular component, in order to select a ultrasonic speed which provides an acceptable accuracy for each thickness range. Due to these readjustments, the measurement process is slow and complex.
Additionally, some aircraft components like wings skin covers, are typically formed by several layers of different materials, like carbon fiber, copper mesh, adhesive layers, excess of resin, etc., so that the total thickness of the component in a specific area, is the carbon fiber thickness plus the thickness of the other materials.
Since ultrasound propagation speed changes for each type of material (see FIG. 2), the lack of homogeneity of these components, the surface roughness, in addition to the different thicknesses of the component, causes that the accuracy required for dimensional measurements, is not guaranteed. Currently, the error caused by the additional materials different than carbon fiber is disregarded.